---
title: "Shifting control in stage-discharge relation"
subject: "Engineering Hydrology"
chapter: 4
key: "semester_5/engineering_hydrology:shifting-control"
source: https://www.bctengineer.com/q/semester_5/engineering_hydrology/shifting-control
site: BCT Engineering
---

# Shifting control in stage-discharge relation

Engineering Hydrology · Chapter 4: Surface Runoff

- Asked in: 2076 Asoj, 1+2 marks
- Video: [UNDERSTANDING STREAMFLOW AND RATING CURVES | Hydrology 101 Lesson 10](https://www.youtube.com/watch?v=rbpAvw2g05E) — Clear Creek Solutions
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/engineering_hydrology/shifting-control
- Whole chapter: https://www.bctengineer.com/md/semester_5/engineering_hydrology/chapter-4

## Question

Define shifting control in stage discharge relationship. What are the causes of shifting control?

## Short answer

A shifting control means the stage-discharge relation changes over time. Causes include scour/deposition of bed, vegetation growth, moving bedforms, debris, bank erosion, backwater effects, hysteresis, and human activities.

## Answer

#### Definition
A **shifting control** is a control (the channel feature that governs the stage-discharge relation) that changes with time, so the stage-discharge relation at the gauging section is not constant. The same stage gives different discharges at different times.

#### Causes of shifting control
1. **Scour and deposition** of the alluvial (sand, silt) bed by the flow, the commonest cause: aggradation lowers the discharge for a given stage, degradation raises it.
2. **Growth and decay of aquatic vegetation** or crops in the channel, which change roughness.
3. **Moving bed forms** (dunes, ripples) in sandy rivers.
4. **Debris, boulders or ice** jams at the control.
5. **Changes in bank shape** due to erosion or collapse.
6. **Backwater effects** from tributaries, downstream structures or tides.
7. **Variable slope (hysteresis)** between rising and falling floods; the rising stage gives more discharge than the falling stage for the same stage.
8. **Human activity** such as sand mining, bridge or weir construction, and dredging.

For such sections frequent discharge measurements are made and the shift is corrected with time.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. A shifting control means
   A. Discharge is always constant
   B. The control does not change
   C. The gauge moves downstream
   D. The control changes with time so the stage-discharge relation is not constant
   Answer: D. The same stage gives different discharges at different times. (Key point: Definition)

2. What is the commonest cause of shifting control?
   A. Scour and deposition of an alluvial bed
   B. Evaporation
   C. Wind
   D. Change of rainfall
   Answer: A. Scour and deposition of sand and silt beds change the channel geometry at the control. (Key point: Commonest cause)

3. If the bed aggrades at the control, what happens to discharge for a given stage?
   A. It becomes zero
   B. It decreases
   C. It increases
   D. It is unchanged
   Answer: B. Aggradation raises the bed so the same stage passes less discharge; degradation does the opposite. (Key point: Aggradation effect)

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